Conway, South Carolina - Donald Trump threatened to leave NATO partners open to Russian attacks if they don't pay up, in statements that the Biden White house called "unhinged."

Trump, campaigning in Conway, South Carolina ahead of the GOP primary on February 24, claimed he had told NATO members that they shouldn't count on US support if they don't meet their financial obligations.

"I said, 'Everybody’s gonna pay.' They said, 'Well, if we don't pay, are you still going to protect us?' I said, 'Absolutely not,'" he boasted, adding: "They couldn’t believe the answer."

What's more, Trump would even "encourage (Russia) to do whatever the hell they want. You gotta pay."

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The White House condemned the comments immediately.

"Encouraging invasions of our closest allies by murderous regimes is appalling and unhinged – and it endangers American national security, global stability, and our economy at home, spokesperson Andrew Bates said in a statement on Saturday.

Biden has "restored our alliances," Bates said, adding that NATO is the "largest and most vital it has ever been."

During a recent visit to Washington, NATO Secretary General Jens Stoltenberg countered fears that a Trump win could jeopardize NATO's future. He had worked with Trump for four years and listened to him carefully, Stoltenberg reportedly told CNN at the end of January.

Trump's main criticism – that alliance partners spend too little on NATO – has been heard, with significant defense spending increases in recent years.

Under Article 5 of the NATO treaty, an attack on one NATO member is considered as an attack on all, and the defense alliance "will take" actions needed to defend the attacked ally.